Furnace doesn’t work with fan it auto

[garyham]

My furnace stopped working a few days back. Troubleshooting I found it worked when I switched the fan to “on” position. (It’s in heating mode). With fan in “auto” I hear a soft hum but it does not ever try and cycle on.

I replaced the capacitor thinking this might be the culprit, no change.

furnace is a Bryant model CNPVP6024ACAAAAA
if that helps.

I have just been flipping the power on and off the past few days to heat the house up then shut it back off. Any suggestions would be appreciated.

 

[Bannerman]

I misunderstood as I neglected to notice that the motor will run when switched to the ON setting.

Confirm that model number is for the furnace. An online search indicates it is a cased coil (AC coil) normally installed ontop of a furnace.

 

[Sponsor]

 

[garyham]

The fan and the blower spin effortlessly.
What’s confusing to me is why does it run just fine with the fan switched to “on” instead of auto.

 

[Bannerman]

I wanted to search for the appropriate manual so as to determine if the fan Auto-ON switch controls a relay, or if it is connected to a circuit board. As stated, searching for the model number you indicated, only listed AC coils.

 

[Reach4]

In classic designs, a bonnet temperature thermostat told the blower when to turn on when hot or off when cold. Do you have a schematic?

I don't know your furnace.

 

[garyham]

I did give the coil number. the furnace model is 340AAV060120
Does this help?

 

[Reach4]

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/340AAVInstall6.pdf page 33 has a wiring diagram.

 

[garyham]

 

[garyham]

That page (33) looks like the photo I just tried to post from the furnace cover.

 

[WorthFlorida]

What type of thermostat?


https://xtronics.com/wiki/Thermostat_signals_and_wiring.html
Cooling
If there is a call for cool, R is connected to Y (compressor). In air conditioning mode the thermostat controls the fan, so G (Fan) is also connected to R. For cooling, the furnace usually selects the high speed of the blower.

Heating
In conventional heating which is oil or gas, the furnace controls the fan, so only R is connected to W (heat). For electric heating, the thermostat controls the fan (G), thus in this case both G (Fan) and W (heat) are connected to R (24 VAC). For heating applications, a lower blower speed is used and the furnace selects it.

The furnace controls the fan because oil and gas heat is not instantaneous. In order to avoid a blast of cold air, the furnace controls the fan. It can do this with a simple delay or by temperature set by the limit switch in the plenum.

 

[garyham]

What type of thermostat?


https://xtronics.com/wiki/Thermostat_signals_and_wiring.html
Cooling
If there is a call for cool, R is connected to Y (compressor). In air conditioning mode the thermostat controls the fan, so G (Fan) is also connected to R. For cooling, the furnace usually selects the high speed of the blower.

Heating
In conventional heating which is oil or gas, the furnace controls the fan, so only R is connected to W (heat). For electric heating, the thermostat controls the fan (G), thus in this case both G (Fan) and W (heat) are connected to R (24 VAC). For heating applications, a lower blower speed is used and the furnace selects it.

The furnace controls the fan because oil and gas heat is not instantaneous. In order to avoid a blast of cold air, the furnace controls the fan. It can do this with a simple delay or by temperature set by the limit switch in the plenum.

I was able to get it going over the weekend. thermostat may be having issues is all i can think of now. i have two thermostats on the furnace with a couple dampers that open and close as they call for air. the main thermostat was the one not working while the other is in the off position as it is only for a bonus room that is not used and is upstairs so it still stays warm enough. so in trouble shooting i turned that one on and the main one off then after it switched over and ran for a few minutes i switched the main one back to auto on the fan then turned it on. that's all it took for it to turn back on and run as normal and has for the past 5 days. not sure why but it works now.

thanks for the input!

 

[WorthFlorida]

Have you checked the combustion air intake? There may be a screen at the inlet and it could be blocked with dust, dirt, leaves, etc.

 

[garyham]

Have you checked the combustion air intake? There may be a screen at the inlet and it could be blocked with dust, dirt, leaves, etc.

I have not but i will. thanks for the tip.